This invention relates to power lawn edgers, and more particularly to lawn edgers having an adjustable rotary cutting blade.
Typical lawn edgers in the prior art have a belt-driven cutting blade on an adjustable arm, the arm providing for selection of both cutter height and blade cutting angle. Usually, a selection of cutter blade angles between vertical and horizontal is provided.
In order to provide wheel support of the lawn edger at a point near the cutting blade, for both the vertical and the horizontal blade position, some lawn edgers in the prior art have a supporting wheel that can be laterally positioned to provide close support near the blade in the vertical position and clearance for the blade in the horizontal position.
The lateral wheel adjustment mechanisms for lawn edgers in the prior art have numerous disadvantages. For example, one arrangement permitting lateral adjustment of the wheel comprises a supporting wheel slideably mounted on a long, transverse axle. A slotted spacer that can be attached to the axle is used to retain the wheel at a selected end of the axle. Lateral adjustment of the wheel is performed by removing the spacer from the axle, sliding the wheel on the axle, then replacing the spacer on an opposite side of the wheel.
A disadvantage of this prior art arrangement is that the spacer is difficult to remove and replace on the axle. An operator must reach down near ground level, grasp the spacer, rotating it so that he can pull in a direction opposite the slot, then remove the spacer against an interference fit between the slot and the axle. When replacing the spacer, the operator must, while avoiding movement of the wheel from one end of its travel, position the slot of the spacer against the axle, then push the spacer over the axle against the interfernce fit.
Another disadvantage of this prior art arrangement is that the wheel is difficult to slide along the axle, especially when there has been an accumulation of dirt and debris from operation of the lawn edger. On one hand, the wheel tends to bind on the axle when it is pushed laterally at an outside point; on the other hand, axle supporting members interfere with pushing laterally at a point near the axle, and an operator can produce only limited lateral force near ground level where the wheel is located.
Another disadvantage of this prior art arrangement is that the axle and support therefor, being fixedly mounted to the lawn edger, must be positioned to clear the blade in all blade orientations. The cutting blade of lawn edgers in the prior art can be lifted above a normal cutting height for disengaging drive power from the blade. This requires that the blade, when oriented horizontally, be lifted past the axle without colliding therewith. In order to permit lateral movement of the wheel reasonably close to the blade when the blade is oriented vertically, the axle must be located about 6 inches to the rear of the blade axis. Because the axle is located about 6 inches behind the blade axis, the lawn edger is awkward to maneuver, and the blade, when oriented vertically, generates a wide ditch while cutting around corners.
A further disadvantage of this prior art arrangement is that the spacer might be jarred loose from the lawn edger or otherwise become lost.
In another example of the wheel adjustment mechanisms in the prior art, the wheel is mounted on a carriage, and the adjustment is performed by loosening a locking thumb screw, sliding the carriage laterally along a square, tubular bar, and then tightening the thumb screw against the bar.
A disadvantage of this prior art arrangement is that the carriage tends to bind on the bar, making the adjustment difficult. This is because the wheel is cantilevered from the bar, producing large force reactions against the bar, even when the lawn edger is lifted to raise the wheel from the ground. It is difficult to apply sufficient lateral force to the carriage, at a point proximate to the bar, located near ground level, to overcome this binding of the carriage.
Another disadvantage of this prior art arrangement is that it is unsafe in that the thumb screw tends to vibrate loose, becoming ineffective. Left unattended, the thumb screw will work completely free, possibly becoming lost. More seriously, the carriage may move into the path of the blade, with a danger of injury to the operator from being struck by flying fragments. Therefore, the thumb screw must be severely tightened, a difficult operation likely to cause permanent deformation of the bar and premature failure of the thumb screw.
Thus there is a need for a lawn edger wheel mechanism for lateral adjustment of a supporting wheel that provides support of the edger close to the blade, has no loose parts which may become lost, and is both safe and easy to use.